Field
This invention relates generally to a phased array transducer for inspecting a fastener hole in a structure and, more particularly, to a phased array transducer for inspecting a fastener hole in a structure without removing the fastener, where the transducer includes a plurality of transducer elements that are scanned to image the entire thickness of the structure.
Discussion
For many industries, such as the aerospace and aircraft industries, the structural integrity of many vehicle and system components is important. Thus, it is very important in those industries that reliable techniques are available to examine the integrity of the structural components, such as the skin of the aircraft to ensure that the aircraft does not suffer from structural failure when in flight. Therefore, various techniques have been developed for the non-invasive and non-destructive analysis of different structural components and materials to detect for wear, fatigue, corrosion, cracking, etc. in the aircraft and other industries.
One known technique for inspecting a component for defects employs an electromagnetic coil that induces eddy currents in the component. The complex impedance in the coil changes as the eddy current encounters defects in the component, which can be observed on an oscilloscope. Other non-destructive inspection techniques are also known to those skilled in the art.
Most aircraft and other structural components employ fasteners, such as bolts, rivets, structural pins, etc., to hold an assembly of component layers or parts together. When a structure is loaded with these types of fasteners, high stress points are often created that can crack the structure at the fastener locations. For example, after years in service, corrosion often occurs around an opening for a fastener because the fastener is often made of steel and the part is often made of aluminum.
The current techniques for inspecting the area around the hole that a fastener is inserted usually require that the fastener be removed from the structure, such as by drilling out the fastener. An inspection probe is then inserted into the hole and manipulated so that the entire thickness of the component around the hole is inspected. The removal of the fastener can result in tremendous damage to the fastener, nut, finishes and structure adding cost to the inspection process. Further, many structures require disassembly, particularly in the case of multilayer structures that require all layers to be inspected not just the outer layers. In the case of sealed laminate aircraft structures, such as an aircraft keel beam, the removal of the keel beam requires that the aircraft be shored up to support the existing structure and load transfer due to the keel beam structure being removed. Known inspection processes also often require expensive tooling, which must be specially designed, therefore adding additional cost to the inspection process.
One known inspection system that does not require the fastener to be removed from the hole is known in the art as an automated fastener-hole imaging system (AFIS). The AFIS employs a phased array ultrasonic probe, but requires an expensive alignment mechanism to rotate the probe around the fastener. Further, the AFIS needs to be adjusted every time a different fastener size is encountered, thus making the AFIS impractical for many applications involving multi-size fasteners or holes. Additionally, the AFIS needs to be set up and adjusted every time a different fastener hole is be inspected, which makes the inspection process using the AFIS both time-consuming, labor intensive and, in many cases, impractical. Thus, there is a need in the art for an inspection system for inspecting fastener holes while the fastener is still positioned in the hole that is cost effective, less complicated, more versatile, less labor intensive, etc.